1. Field of the Invention
This invention relates to the coating of glass fibres, and more particularly to a method of coating glass fibres to protect them from deterioration in an alkaline environment, such as a Portland cement matrix. The invention also relates to glass fibres coated by the method of the invention, to an aqueous coating composition for use in the method of the invention and to cement composite materials formed by incorporating the coated glass fibres in a cement matrix.
2. Description of the Prior Art
The use of glass fibres as a reinforcing material in cement has become practicable since the development of alkali-resistant glass fibres such as those made from glass compositions as described and claimed in our British Patent specification No. 1,290,528 and sold under the Trade Mark "Cem-FIL" by Fibreglass Limited. Alkali-resistant glass fibres may be of varying durability according to the composition of the glass from which it is formed. The aggressiveness of the environment may also vary; for example, the durability obtained under dry conditions is better than that achieved when glass fibre reinforced cement composites are exposed to natural weathering in the open. It can be necessary in some circumstances to achieve a greater durability than is possible by alterations in glass composition, or to improve the durability of a glass without increasing the cost of the batch ingredients. We have described in our British Patent specification No. 1,465,059 the use of coating compositions for glass fibres comprising a protective material to reduce deterioration of the glass fibres when incorporated in cementitious products, the protective material consisting of at least one monocyclic or polycyclic aromatic compound which has at least three hydroxyl groups on the aromatic ring or, in a polycyclic compound, on at least one of the aromatic rings. We have found such protective materials to confer on the glass fibres increased durability in an inorganic cement matrix. Co-pending United States Patent Application Ser. No. 708,977, now U.S. Pat. No. 4,123,287, describes the use of coating compositions containing, as a protective material, at least one dihydroxybenzoic acid which we have found to confer increased durability on glass fibres in an inorganic cement matrix. Co-pending United States Patent Application Ser. No. 646,082, now U.S. Pat. No. 4,062,690, describes a method of increasing the effect of the protective materials described in our British Patent specification No. 1,465,059 or U.S. Application Ser. No. 708,977, by incorporating them into a coating composition with a partially-cured A-stage phenol-formaldehyde resin of the water-dilutable resole type, which is subsequently cured. This is believed to trap the protective material, probably by both chemical and physical means, in the cured resin matrix, from which it can be slowly released.
If the protective material, i.e., the hydroxy compound or compounds, is merely dispersed in a carrier and then coated on to the fibre, it has been found difficult to ensure that the material remains on, or in the vicinity of, the fibre surface during the various operations carried out during the formation of a cement composite.